With a technical revolution in recent years that high density of magnetic recording medium has been realized, the magnetic tape cassettes and video tape recorders (VTR) have become compact. There are many occasions where the VTR is used outdoors to take pictures of landscapes and portraits. In order to obtain dust proofing property enough to withstand such outdoor uses, some magnetic tape cassettes have lids of two panel type or three panel type for covering a front face and a back face of the magnetic tape. There are various types of the magnetic tape cassettes and, the DVC for example includes a small size (S type), a medium size (M type), and a large size (L type).
FIG. 23 is an exploded perspective view of the DVC of the M type provided with the lid of three panel type. A cassette case of this magnetic tape cassette 310 is composed of an upper cassette half 311 and a lower cassette half 312 each of which includes a flat plate and upright walls surrounding the flat plate.
The flat plate of the lower cassette half 312 is formed with reel holding holes 313 on which a pair of reels 319 are mounted having a magnetic tape T wound around them. Reel driving shafts provided in a hardware such as VTR and so on are adapted to be inserted into the reel holding holes 313. At a center of a forward end of the cassette case (a side opposed to a head of the hardware when the magnetic tape cassette has been loaded in the hardware), there is formed an opening 314. The flat plate of the lower cassette half 312 is provided with tape guides 318 at both sides of the opening 314. The surrounding walls of the lower cassette half 312 are provided with cutouts 317 for enabling the magnetic tape T which is wound around the reels 319 to pass into and out from the opening 314 at the other sides of the tape guides 318 opposite to the opening 314. At a center of a forward end of the flat plate of the lower cassette 312 and behind the opening 314, there is provided a central part 315 of a front wall which projects toward the upper cassette half 311. The flat plate of the lower cassette half 312 is further provided, at both sides of the central part 315, with lower walls 315a which constitute both side parts of the front wall in combination with upper walls 315b of the upper cassette half 311. The opening 314 is defined by this front wall and the tape guides 318.
To the cassette case composed of the upper cassette half 311 and the lower cassette half 312 assembled together, is attached an open/close lid 320 so as to cover the magnetic tape T which is stretched between the tape guides 318 (over the opening 314). This open/close lid 320 consists of an outer lid (a front lid) 321, a top lid (an upper lid), and an inner lid (a back lid) 323.
The outer lid 321 includes a front lid plate 321a covering a front face of the magnetic tape T which is stretched over the opening 314, and side plates 321b which extend backward from both sides of the front lid plate 321a. Pivotal pins 321c having distal end flanges are provided so as to project from inner faces of the side plates 321b. These pivotal pins 321c are rotatably held by pin holding cutouts 324a which are formed in pin supporting pieces 338a provided at front sides of both lateral walls 311a of the upper cassette half 311. The pivotal pins 321c are rotatably engaged and held in pin holding holes which are defined by the pin holding cutouts 324a in the pin supporting pieces 338a of the upper cassette half 311 and by pin supporting pieces 338b of the lower cassette half 312. The outer lid 321 can rotate around the pivotal pins 321c. The outer lid 321 is always urged by a lid spring 327 in a closing direction.
The top lid 322 includes an upper lid plate 322a covering an upper edge of the magnetic tape T which is stretched over the opening 314, and side plates 322b which extend downward from both sides of the upper lid plate 322a. At forward sides of inner faces of the side plates 322b, there are provided front lid connecting pins 322c adapted to rotatably connect the upper lid plate 322a to connecting holes 321d of the front lid plate 321a. At backward sides of the inner faces of the side plates 322b, there are provided slide pins 322d which are adapted to be slidably engaged with cam grooves 325 for the upper lid which are formed in both side walls 311a of the upper cassette half 311. When the outer lid 321 is opened, the top lid 322 moves backward of the cassette case while the slide pins 322d are moved along the cam grooves 325 for the upper lid, and the upper lid plate 322a is maintained in substantially parallel to an upper face of the cassette.
The inner lid 323 includes a back lid plate 323a covering a back face of the magnetic tape T which is stretched over the opening 314. From both ends of an upper edge of the back lid plate 323a, are projected upper lid connecting pins 323b adapted to rotatably connect the back lid plate 323a to the upper lid plate 322a. From both ends of a lower edge of the back lid plate 323a, are projected slide pins 323c adapted to be slidably engaged with S-shaped cam grooves 326 for the inner lid which are formed on opposed faces (inner faces) of a pair of the tape guides 318 provided on the lower cassette half 312. The upper lid connecting pins 323b follow the movement of the top lid 322 when the outer lid 321 is opened. Along with the movement of the upper lid connecting pins 323b, the slide pins 323c are caused to slide inside the cam grooves 326 for the inner lid.
When this magnetic tape cassette 310 has been loaded in the hardware, the side plates 321b of the outer lid 321 are pushed upward against an urge of the lid spring 327 by means of lid opening pins (not shown) provided on the hardware. In association with the lid opening motion of the outer lid 321, on this occasion, the top lid 322 and the inner lid 323 perform their lid opening motions. When the magnetic tape cassette 310 has been taken out from the hardware, the lids 321, 322 and 323 will perform the lid closing motions by the urge of the lid spring 327.
FIG. 24 is an enlarged view showing an area around the tape guides 318. As shown in FIG. 24, on an inner face of one of the tape guides 318 which is opposed to the other tape guide (not shown), there is formed the cam groove 326 for the inner lid in which the slide pin 323c of the aforesaid inner lid 323 is adapted to slide. Also on the inner face of the tape guides 318, there is provided a projection 328 which is formed with a position detecting hole (a reference hole) of the magnetic tape cassette.
By the way, the upper cassette half 311 and the lower cassette half 312 of this magnetic tape cassette are formed by injection molding. In order to prevent occurrence of molding sinks on a guide face 318a of the tape guide 318 on occasion of the injection molding, molding sink preventing recesses must be formed on a back face (the inner face) 318b of the guide face 318a. In the tape guide 318 having such a shape as shown in FIG. 24, a molding sink preventing recess 329a is formed in an area of the back face 318b of the tape guide 318 in front of the cam groove 326 for the inner lid (outside of the cassette case). Also in an area of the back face 318b in rear of the cam groove 326 for the inner lid (inside of the cassette case) and above the projection 328 formed with the position detecting hole 328a, there is formed a molding sink preventing recess 329b. Still further, in an area of the back face 318b of the tape guide 318 in rear of the cam groove 326 for the inner lid and in front of the projection 328 formed with the position detecting hole 328a, there is formed a molding sink preventing recess 329c. 
Because of existence of the three molding sink preventing recesses and the cam groove 326 for the inner lid as described above, high friction resistance will be created in molds (slide cores) for forming these three molding sink preventing recesses and the cam groove 326 for the inner lid, when they slide. In a manufacturing process of the lower cassette half 312, a number of the lower cassette halves must be molded by employing these slide cores, and therefore, the slide cores will be subjected to the high friction resistance repeatedly. It has been found that these repeated loads lead to the following problems of the slide cores.
FIG. 25 is a sectional view taken along a line A—A of FIG. 24 showing a slide core 390 for forming the molding sink preventing recesses and the cam groove 326 for the inner lid. Among the molding sink preventing recesses, the molding sink preventing recess 329c is small in size. As shown in FIG. 25, a portion 390c of the slide core 390 adapted to form the molding sink preventing recess 329c is narrow and long. Accordingly, the portion 390c of the slide core 390 adapted to form the molding sink preventing recess 329c tends to be broken at a root 390r, and has extremely low durability. When the portion 390c of the slide core 390 adapted to form the molding sink preventing recess 329c has been broken, the broken portion 390c will hinder motions of the mold, and the broken mark of the mold will be transferred to an area of the tape guide 318 to be formed with the molding sink preventing recess 329c, thus resulting in bad outer appearance.
A first object of the present invention is to provide a magnetic tape cassette in which durability of the molds can be enhanced.
FIG. 26A is a sectional view of an essential part of the above described upper cassette half 311 taken along a center line in a longitudinal direction. FIG. 26B is a sectional view of an essential part of the above described lower cassette half 312 taken along a center line in a longitudinal direction. As shown in FIG. 26A, the upper cassette half 311 is provided with an upper lid 330 above a tape running area. In areas of the upper cassette half 311 adjacent to the opening 314, there are provided cam covers 331 in a shape of flat plate which will prevent the slide pins 323c of the inner lid 323 from moving upward out of the cam grooves 326 for the inner lid. In areas of the cam covers 331 adjacent to the opening 314, there are respectively formed the upper walls 315b which constitute both the side parts of the front wall of the cassette case in combination with the lower walls 315a of the lower cassette half 312. The upper walls 315b are provided with projections 332 formed with respective positioning reference holes 332a so as to project forward.
Meanwhile, as shown in FIG. 26B, the lower walls 315a of the lower cassette half 312 are also provided with the projections 328 formed with the reference holes 328a so as to project forward near the cam grooves 326 for the inner lid. These projections 328 are in contact with the back faces 318b of the tape guides 318 too.
In order to assemble the magnetic tape cassette 310 employing the open/close lid 320 of the three panel type as shown in FIG. 23, the outer lid 321, the top lid 322 and the inner lid 323 are temporarily assembled in advance. Then, the temporarily assembled three lids 321, 322, 323 are assembled to the upper cassette half 311, by engaging the slide pins 322d of the top lid 322 in the cam grooves 325 for the upper lid formed in the upper cassette half 311, and at the same time, by engaging the pivotal pins 321c of the outer lid 321 with the pin holding cutouts 324a formed in both the side walls 311a of the upper cassette half 311. Then, as shown in FIG. 27, the upper cassette half 311 is assembled to the lower cassette half 312 which has been placed on a support table in a state where the open/close lid 320 is fully opened.
By the way, when the upper cassette half 311 is assembled to the lower cassette half 312 through manual operation, there may be some occasions where the upper cassette half 311 is happened to be assembled to the lower cassette half 312 while the upper cassette half 311 is not in parallel to a support face of the lower cassette half 312. In this case, because the inner lid 323 is rotatably connected to the top lid 322 only by means of the upper lid connecting pins 323b, the inner lid 323 often tends to be displaced from a proper position around the upper lid connecting pins 323b. As the results, the slide pins 323c of the inner lid 323 are moved and cannot be inserted into the cam grooves 326 for the inner lid, so that the upper cassette half 311 may not be accurately assembled to the lower cassette half 312.
A second object of the present invention is to provide a magnetic tape cassette in which assembling performance of the open/close lid can be enhanced.
As shown in FIG. 23, lock projections 321e are provided so as to project from the inner faces of the side plates 321b of the outer lid 321. To both side walls of the lower cassette half 312, are rotatably fastened lid lock members 335a, 335b which are adapted to be engaged with these lock projections 321e to lock the open/close lid 320 in the closed state. One of the lid lock members 335a is urged by the lid spring 327 mounted on the pivotal pin 321c of the outer lid 321 in a direction of locking (a locking direction) the open/close lid 320. The other lid lock member 335b is urged in a locking direction by a lid lock spring 334 which is assembled to the lower cassette half 312.
FIG. 28 is a view showing an outer face of the side walls of the cassette case. The outer lid 321 includes the front lid plate 321a covering the front face of the magnetic tape T which is stretched over the opening 314, and the side plates 321b extended from both sides of the front lid plate 321a. The pivotal pins 321c having the distal end flanges 333 are provided on the inner faces of the side plates 321b perpendicularly to the inner faces. The pivotal pins 321c are rotatably engaged and supported in the pin holding holes 324 which are defined by the pin supporting pieces 338a of the upper cassette half 311 and the pin supporting pieces 338b of the lower cassette half 312. The outer lid 321 can rotate around the pivotal pins 321c. 
The lid spring 327 is mounted on the side plate 321b of the outer lid 321. The lid spring 327 includes a multiplied coil portion 327c which is idly mounted around the pivotal pin 321c, one leg portion 327a which is locked on a spring hook projection 336 provided on the side plate 321b, and the other leg portion 327b which is locked on a spring hook projection 337 provided on the side wall of the upper cassette half 311. In other words, the lid spring 327 is locked with the side plate 321b of the outer lid 321 at its one leg portion 327a, and locked with the side wall of the upper cassette half 311 at its other leg portion 327b. With biasing force in a direction toward a bottom face of the cassette (a direction D) generated by the leg portions 327a, 327b of this lid spring 327, the outer lid 321 is urged in a closing direction (a direction C). Meanwhile, the leg portion 327b of the lid spring 327 is engaged with an upper face of the lid lock member 335a (See FIG. 23) from a side of the upper cassette half 311 thereby to urge the lid lock member 335a in a locking direction.
When the open/close lid 320 is opened or closed, the slide pins 323c of the inner lid 323 are guided by the cam grooves 326 for the inner lid which are formed on the tape guides 318 of the lower cassette half 312 so as to move the inner lid 323 along the inner faces 318b of the tape guides 318 as shown in FIG. 29. An upward movement of the inner lid 323 will be restrained by the cam covers 331 which are provided on the upper cassette half 311.
However, since the upper cassette half 311, the lower cassette half 312, and the lids are separately molded, there exist manufacturing errors between the components. In case where the inner lid 323 is offset to one side due to a manufacturing error when assembled, a portion of the inner face 318b (an area having a knitted pattern) of each of the tape guides 318 interferes with the side face of the inner lid 323. This will hinder smooth opening and closing motions of the open/close lid, and an occurrence of abrasion powder by the interference will result in errors such as a drop out and so on. Moreover, a force for opening and closing the open/close lid may rise with the interference, or the force for opening and closing the open/close lid may vary with the interference.
A third object of the present invention is to provide a magnetic tape cassette in which opening and closing motions of the open/close lid can be performed smoothly, and errors such as a drop out and so on can be prevented, and damage caused by a shock of falling down can be reduced.
By the way, the spring hook projection 336 provided on each of the side plates 321b of the outer lid 321 as shown in FIG. 28 also moves at the opening and closing motions of the open/close lid. FIG. 30 is a view showing the front side of the magnetic tape cassette 310 partly cut away. The spring hook projection 336 moves along an outer face 339a of the pin supporting piece 338a of the upper cassette half 311, and along an outer face 339b of the pin supporting piece 338b of the lower cassette half 312. These outer faces 339a, 339b of the pin supporting pieces 338a, 338b are preferably flush with each other so that they may not make obstacles to the opening and closing motions of the open/close lid.
However, because the upper cassette half 311 and the lower cassette half 312 are separately molded and assembled, these outer faces 339a, 339b of the pin supporting pieces 338a, 338b are not always made flush, but in some cases, a step-like difference E may be formed between these outer faces as shown in FIG. 31. It is difficult to completely eliminate this step-like difference E from a reason of molding work. Since the spring hook projection 336 interferes with the step-like difference E, the spring hook projection 336 will not move linearly, but move as shown by crooked arrow marks O and C in FIG. 31. This will hinder smooth opening and closing motions of the open/close lid 320, and an occurrence of abrasion powder by the interference will result in errors such as a drop out and so on. Moreover, a force for opening and closing the open/close lid may rise with the interference, or the force for opening and closing the open/close lid may vary with the interference.
A fourth object of the present invention is to provide a magnetic tape cassette in which opening and closing motions of the open/close lid can be performed smoothly, and errors such as a drop out and so on can be prevented.
As shown in FIG. 23, in order to confirm from the exterior an amount of the magnetic tape T wound around one of the reels 319, there is formed an opening which extends in a lateral direction of the flat plate of the upper cassette half 311 at one side in a longitudinal direction (a right side in the drawing) of the flat plate. A transparent window member 340 is attached to the upper cassette half 311 so as to cover the opening.
The cam groove 326 for the inner lid which is provided on each of the tape guides 318 is formed in a curved shape at its front side and in a shape of a straight line at its back side as shown in FIG. 32, so that it may not hinder the smooth opening and closing motions of the outer lid 321. As the open/close lid 320 is gradually opened from a state in FIG. 32, the front side of the top lid 322 supported by the outer lid 321 will be raised drawing a circular orbit, and at the same time, the back side of the top lid 322 will be raised along an arc shaped portion at the front side of the cam groove 325 for the upper lid with which the slide pin 322d is engaged. As the outer lid 321 rotates into a state where it has rotated about 90 degree (an open state), the front side of the top lid 322 will be raised rectilinearly, and the back side of the top lid 322 is moved along the straight portion at the back side of the cam groove 325 for the upper lid. In this manner, the top lid 322 moves backward of the cassette case as shown in FIG. 33, while the upper lid plate 322a is maintained in parallel to the upper face of the cassette and the slide pin 322d is not caught by the cam groove 325 for the upper lid.
However, while the opening and closing motions of the open/close lid 320 are repeated, abrasion may occur between the cam groove 325 for the upper lid and the slide pin 322d of the top lid 322. Conventionally, a width of the cam groove 325 for the upper lid has been made constant from the curved portion to the straight portion so as to smoothly guide the slid pin 322d inside the cam groove 325 for the upper lid. A gap between the cam groove 325 for the upper lid and an outer peripheral face of the slide pin 322d has been conventionally set to be 0.1 mm so that the slide pin 322d may not rattle in the cam groove 325 for the upper lid. Nevertheless, abrasion has occurred between the cam groove 325 for the upper lid and the slide pin 322d. Abrasion powder generated from the abrasion will be a cause of the drop out and so on.
A fifth object of the present invention is to provide a magnetic tape cassette which is free from abrasion between the cam grooves and the slide pins.
As shown in FIG. 23, an ID board 350 which is an electric circuit board of a slim type is incorporated in the magnetic tape cassette 310. In such a small sized product as this magnetic tape cassette 310 which incorporates electric circuits, a thin mounting board which requires less occupying space is employed as the electric circuit board.
The ID board 350 is a component for identifying kind and use of the magnetic tape T. The ID board 350 is assembled to a corner area at the back side of the lower cassette half 312. According to cases, an ID board incorporating an integrated circuit (IC) for storing managing information of recorded contents, which may be called as an IC board, may be assembled. FIG. 34 is an enlarged view of a structure of the ID board 350 to be assembled to the lower cassette half 312. the ID board 350 has a board plate 350a formed in a substantially L-shape. There are provided electrical contacts (plated terminals) 351a, 351b, 351c and 351d in a rectangular shape on a back face (a face in the depth in the drawing) of the board plate 350a. On the other hand, on a front face (a face in the front in the drawing) of the board plate 350a, there are provided chip resistors 353a, 353b. The board plate 350a is provided with through holes 352. The electrical contacts 351a to 351d on the back face of the board plate 350a and the chip resistors 353a, 353b on the front face of the board plate 350a are electrically connected by way of a printed wiring 354.
A space for containing the ID board is formed at a position in the lower cassette half 312 adjacent to the back wall. The back wall is provided with openings 312a which are defined by frames, at positions corresponding to the contacts 351a to 351d on the back face of the ID board 350. When the ID board 350 has been assembled in the ID board containing space, the contacts 351a to 351d are respectively exposed to the exterior of the cassette case through the openings 312a. 
When the magnetic tape cassette provided with the ID board has been loaded in a hard ware which is not shown, terminals of the hardware get in touch with the contacts 351a to 351d on the back face of the ID board 350 and read out resistance values between the determined two contacts. On the basis of these resistance values, the hardware identifies the type and use of the magnetic tape. Similarly, when the magnetic tape cassette provided with the IC board has been loaded in the hardware, although not shown, terminals of the hardware get in touch with the contacts on the back face of the IC board to provide required information to the hardware.
By the way, the thin and small mounting board is generally manufactured, for the purpose of saving manufacturing cost, by making a plurality of electric circuits having the same structure on a large sized board sheet, and then, by dividing the board sheet. A plurality of the ID boards 350 can be taken out from an ID board sheet 360 as shown in FIG. 35. This ID board sheet 360 can provide 54 pieces of the ID board 350. Each of the ID boards 350 is connected to connecting members 361 at two or three positions of an outer circumference of the ID board.
Steps of taking a plurality of the ID boards 350 from this ID board sheet 360 will be described. As a first step, the ID board sheet 360 is carried to a mounting section which is not shown, with the face having the contacts 351a to 351d directed downward, and the determined chip resistors are mounted on its upper face, that is, a face opposite to the face provided with the contacts 351a to 351d. 
Then, the ID board sheet 360 is carried to a measuring section which is not shown, in a state where the face having the contacts 351a to 351d is still directed downward. Then, measuring terminals are brought in touch with the contacts 351a to 351d from the underneath of the ID board sheet 360, thus measuring resistance between the two determined contacts.
Then, the ID board sheet 360 is carried to a press section which is not shown, in a state where the face having the contacts 351a to 351d is still directed downward, and a cutting edge is applied to the ID board sheet 360 from the above of the relevant ID board sheet to cut off the ID boards 350 from the connecting members 361.
Recently, in order to improve productivity of the slim electric circuit board, it has been desired to obtain the board sheet having a further large size, and to cut off a large number of slim boards of electric circuits at one time. For example, in the above described ID board for the magnetic tape cassette, it is sometimes required that 100 to 200 pieces of the ID boards are taken from a sheet of the ID board sheet. However, as a result of upsizing the ID board sheet, it is feared that the ID board sheet may be deflected during the transfer to the press section, and flat ID boards cannot be obtained in the press section.
In this situation, it has been considered that the chip resistors are mounted in a state where a reinforcing plate is attached to the back face of the ID board sheet 360 (the face provided with the contacts 351a to 351d). However, when such reinforcing plate has been employed, the contacts on the ID board sheet are covered with the reinforcing plate, and cannot get in touch with the measuring terminals in the measuring section.
Moreover, in the conventional steps of taking the ID board 350 from the ID board sheet 360, the measuring terminals have been abutted against the contacts of the relevant ID board sheet from below of the ID board sheet 360. However, in order to support the ID board sheet so as to permit the access of the measuring terminals from the below, a complicated mechanism has been required. Therefore, it has been considered that the ID board may be turned upside down while it is carried to the measuring section, which however, would incur a further complication of the mechanism.
A sixth object of the present invention is to provide a magnetic tape cassette which is provided with a slim electric circuit board of which productivity can be improved.